"IPv6 is being enabled and kept on by more than 1,500 Web sites and ISPs in 22 countries," said Arbor Networks, a company that monitors global Internet traffic closely.

Internet Protocol version 6 has one big improvement over the prevailing IPv4 standard it's designed to supplant: room to grow. However, moving to IPv6 isn't simple, which is why many organizations on the Internet have banded together for Wednesday's World IPv6 Launch event overseen by a standards and advocacy group called the Internet Society.

In practice, IPv6 has been gradually arriving on the Net already, and there's a long way to go after the event. But the launch day is a real milestone. Here's a look at some of the issues involved.

Why all the IPvWhatever fuss?
Because the Internet is running out of room.

Today, IPv4 is used to describe the network address to almost all smartphones, PCs, servers, and Internet-enabled refrigerators so that other devices can exchange data. For example, your computer needs to know the IP address of CNET News to read this story, and CNET's server needs to know your computer's IP address to send the Web page information to it.

IPv4, though, offers only 4.3 billion addresses (2 to the 32nd power, or 4,294,967,296, to be precise). That may sound like a lot, but there are ever more devices to connect to the Internet, and many of the IPv4 addresses are inaccessibly squirreled away by organizations that got large tracts of them earlier in the history of the Internet.

The upshot is that the problem called IPv4 address exhaustion is real: the pipeline of new ones is emptying out. That's a problem for businesses that want to set up new Internet services or for carriers wanting to sell another few million smartphones.

IPv6 to the rescue! It offers 340 undecillion addresses (2 to the 128th power, or 340,282,366,920,938,463,463,374,607,431,768,211,456, to be precise).

There's only one problem: Upgrading the Internet to IPv6 -- and that means the entire Internet -- is expensive, requires a lot of work, and is something most of the computing industry has been putting off until absolutely necessary. There are still procrastinators, but its time now has come.

The Federal Communications Commission shows the relative size of the IPv6 address space enabled by the longer Internet addresses.
FCC

How real is IPv6?
You've been able to create IPv6 networks since 1999, but there's been little point until relatively recently. Many people didn't have computers, home networking equipment, or Internet service providers that could reach IPv6 sites on the Net, and Web sites had little incentive to make their sites available over IPv6.

But that's changing now.

Come Wednesday, somebody with an IPv6 connection will be able to get data from an IPv6 Internet site. The fraction of Internet traffic will be small but then will grow fast. Yahoo properties that will become IPv6-enabled Wednesday include the main Yahoo.com Web site, My Yahoo, and OMG.

"For the IPv6-enabled sites, I expect to see roughly half a percent," said Jason Fesler, Yahoo's IPv6 evangelist. "In a year, in the realm of 10 to 15 percent."

Through a partnership called Atlas, Arbor Networks scrutinizes anonymous data from 253 Internet service providers, 125 of which carry IPv6 traffic today. Arbor has measured a flow of 10 gigabits per second of IP traffic flowing, said product manager Scott Iekel-Johnson. That's 0.04 percent of the total Internet traffic on Atlas, and 0.09 percent of the traffic on the IPv6-carrying ISPs, he said.

Hurricane Electric, a networking company that's been pushing IPv6 technology and services for more than a decade, is seeing the evidence that the shift to IPv6 is real. "Hurricane Electric's professional services group has seen a more than fivefold increase in people wanting us to provide courses and consulting to help them plan and deploy IPv6 over the last two months," said Owen DeLong, the company's IPv6 evangelist and director of professional services.

And based on its Internet monitoring, Cisco predicts "there will be 8 billion IPv6-capable fixed and mobile devices in 2016, up from 1 billion in 2011," the company said this week. "Globally, 40 percent of all fixed and mobile networked devices will be IPv6-capable in 2016, up from 10 percent in 2011."

Cisco Fellow Mark Townsley said IPv6 support is arriving at the two ends of the network connection, and that will push ISPs and other network companies to add their own support so the IPv6 connection actually can be made

"On the content side, we're seeing 50, 60, or 70 percent of content available over IPv6 available by year end," he said. And though Windows XP doesn't have IPv6 support enabled by default, Townsley said, it'll fade from the scene. "The good news is, while 30 to 40 percent of PCs that don't have IPv6 by default, in the next two years, that's dropping down to fractional numbers -- 1 to 2 percent." Android and iOS devices, along with newer versions of Windows and OS X, already have IPv6 support.

Hurricane Electric has seen steadily increasing IPv6 traffic well before the official World IPv6 Launch event.
Hurricane Electric

Why do we need this World IPv6 Launch event then?
It'll add some pretty high-profile commitments to the transition, making it abundantly clear to laggards that they'd better get with the program. Among changes coming on Wednesday:

 Some ISPs will turn on IPv6 and leave it on so at least 1 percent of their customers will have IPv6 access. Those ISPs include AT&T, Comcast, Time Warner Cable, Free Telecom, Internode, KDDI, and XS4ALL.

 Home network device makers Cisco and D-Link will enable IPv6 by default for their home network devices. Cisco makes the Linksys line of home routers.

 Google, Microsoft, Facebook, and Yahoo will enable IPv6 access to their main Web sites and keep it available. Yahoo also committed to offer Yahoo Sports, Yahoo Mail, and Yahoo Finance over IPv6 in coming months. Several services already are available over IPv6 today, but people must go to a specific and different Web address such as ipv6.google.com. Now just going to google.com will return results over IPv6 if it's possible for the person doing the search to communicate with IPv6.

In practice, the IPv6 launch -- a transition that's been under way for years and that will take years more to complete -- has already begun.

Indeed, even the immediate run up to the IPv6 launch event has increased IPv6 content and corresponding network traffic, Hurricane Electric statistics show.

"The trend leading up to launch day is more likely people turning it on for launch day a little early in order to test and verify things and really be ready for leaving it on as of launch day," DeLong said. "There's no penalty on launch day for having turned it on early, so I think you're seeing people run tests in preparation for launch day. Since they aren't encountering problems when the test, they go ahead and leave the test running."

French ISP Free has been an aggressive adopter of IPv6 networking.
Free

Can't we just fix IPv4?
There are crutches to ease the problem. The biggest one is sharing a single IP address among several devices. If you have a home Wi-Fi network, chances are it's sharing its IP address with your computers, mobile phones, game consoles, Net-connected TVs and set-top boxes, and other network-savvy electronics.

Related stories

This approach is called network address translation, or NAT. It's your Wi-FI router's job to be the traffic cop that oversees outgoing data sent from all these devices and directs incoming traffic to the appropriate device.

One real-world analogy to NAT is a street with 10 addresses. When somebody builds a six-unit apartment building at 8 Elm Street, that street address can be shared by the residents of 8A, 8B, 8C, 8D, 8E, and 8F Elm Street. Another analogy is phone extensions: a company can have a single phone number that leads to 10,000 extensions for individual employees.

On a grander scale, a similar concept exists called carrier-grade NAT, or CGN. This takes place at the Internet service provider level rather than the house level, and it's a lot more complicated.

Great -- with NAT, problem solved, right?
Yes and no. NAT has been a huge help in extending the life of IPv4 while the industry gets its IPv6 act together, but it brings its own problems.

Chief among them is that NAT breaks the ideal network model that a device has an actual address that naturally makes it easy to locate on the Net. NAT obscures addresses, which for some security purposes can be convenient, but for data transfer is a pain.

Here's how John Curran, chief executive of the American Registry for Internet Numbers (ARIN), puts it:

The Internet is built on the "end to end" principle; i.e. the ability of one device to directly reach the other end of the connection. Network address gateways, while functional, do not preserve this property and as a result some applications have problems working reliably through them. This has been proven in the use of NAT in the home marketplace, which has resulted in numerous workarounds being deployed to make games and always-on Internet devices (like cameras and picture frames) work reliably.

Basically, NAT means there are first-class citizens on the network with their own addresses and second-class citizens that are harder to reach. That creates a hierarchy in which services must be designed around a relatively small number of central servers rather than enabling direct communication between any device.

Here's an example DeLong uses to show the shortcomings of NAT:

Today, remote scheduling of a recording on TiVO involves putting the scheduling request into the TiVO web site and TiVO's servers wait for your TiVO to "phone home" and pull down that request, so, your TiVO box is constantly having to check in with TiVO central and if your request is coming up in the next few minutes, it might not actually get communicated to the box. (There's generally about a 2 hour delay in this process in my experience).

Without NAT, there's no reason that you couldn't use an app. to send that request directly to your own TiVO box without even involving TiVO central. Even if it still goes through TiVO central, they could push the request out to the TiVO box instead of waiting for the TiVO box to "call in."

Adds Richard Jimmerson, the Internet Society's director for deployment and operationalization, carrier-grade NAT (CGN) also is likely to add delays called latency in Internet communications:

IPv4 address sharing through CGN requires additional devices and software be placed into use between the user and the content they interact with on the Internet. Early testing has shown this increases latency times for users, slowing down response times between their home and the content they are consuming. In some cases this degraded performance will be acceptable to the user, but in other cases it may not. Some latency-sensitive applications -- such as video streaming, IP based voice services, and online gaming -- may be severely impacted.

So NAT, while useful, is in many ways just a technology to tide people over until IPv6 arrives.

Will there be any trouble come Wednesday?
For a small slice of people, yes, but for the vast majority, no.

Yahoo, which participated in the test and has gargantuan Web traffic, has carefully measured the fraction of its visitors who had problems when IPv6 is enabled. "Weeks before the World IPv6 Day 2011, it was roughly 0.055 percent," Fesler said. "A week after, that number was down to 0.022 percent, with a great number of people learning their systems were 'broken' and taking steps to fix it."

However, the problems have been creeping back, even though people might not know it. "Since last year, we've seen a steady rise back towards 0.030 percent. Since few Web sites have been running IPv6, these users have had no reason to realize anything was wrong."

What's actually going wrong?
For that small fraction, the problem is often within a particular user's grasp, Fesler said:

Most of the issues are local to the user's computer, or the user's home network. The problems may be related to the home wireless router they have - a few early IPv6 implementations did things that were ultimately found to not be in the customer's best interest. Many of these early implementations have updates available.

In other cases, it may be related to the home computer. IPv6 might be enabled in the house -- but the firewall installed on the home computer may not be aware of IPv6 (and block the traffic). Or the customer may have enabled specific transitional technology that allows IPv4-only users to have an IPv6 address using public gateways. These public gateways have no service level agreements; it is often impossible for an end user to know there may be a problem.

Other problems outside a person's control can crop up as IPv6 and IPv4 coexist side by side, with gateway devices trying to bridge between the two. That could show up as slow access to some sites.

For example, a person at home whose ISP assigned an IPv4 address, could try to reach an IPv4-based Web site. But the route in between might require IPv6, in which case hardware would have to wrap up the IPv4 data in IPv6, deliver it to the other side, then unwrap it for delivery to the other computer. That would have to be repeated for each packet of data sent in either direction, slowing network performance and increasing complexity.

Japan in particular has some problems, Yahoo said. That's because some ISPs have deployed IPv6 to let their subscribers access particular services such as phone and television that aren't part of the broader Internet, Fesler said. Traffic to the regular Internet uses IPv4.

That's all well and good -- except that the design fools browsers into thinking IPv6 is available for the Internet when in fact it's only available for a walled garden. That means sluggish Web performance as browsers attempt to connect over IPv6 wait before falling back to IPv4. "There is a roughly 1 second delay for Windows users, before giving up on IPv6 and trying IPv4 instead," Fesler said. "This problem is not just for the connection to the Web site, but also for connections to get images on the page and other resources needed to fully draw the Web site."

Updated at 6:15 a.m. PTto correct that Cisco makes the Linksys line of networking products.

About the author

Stephen Shankland has been a reporter at CNET since 1998 and covers browsers, Web development, digital photography and new technology. In the past he has been CNET's beat reporter for Google, Yahoo, Linux, open-source software, servers and supercomputers. He has a soft spot in his heart for standards groups and I/O interfaces.
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